Glass sheets or panels are conventionally maintained, after fabrication of the glass sheets, and before assembly into products, such as flat panel displays, in cassettes. Similarly, semiconductor wafers are placed in cassettes. Cassettes are essentially boxes sized to accommodate sheets or cassettes of a selected size. In one existing design of cassettes, there are provided projecting inward from the sides of the cassette panel supports. A defined distance separates the panel supports. The defined distance is selected to permit an end effector of a robot to pass between the panel supports, so as to remove or insert the panel in the cassette.
After fabrication, and after various steps during processing, panels, semiconductor wafers, and other materials in sheet form, are tested for a variety of physical, electrical, mechanical and chemical properties. Typically, upon fabrication, the panels or wafers are placed in the cassette by a robot with an end effector that engages the panel or wafer in such a manner as to minimize damage. When it is desired to test the panel or wafer, an end effector of a robot is inserted into the cassette, engages the panel or wafer, and transports the panel or wafer from the cassette to a testing device. The robot then places the panel or wafer on suitable supports on the testing device. A handler in the testing device moves the panel or wafer relative to test heads that carry out various tests on the panel or wafer. Upon completion of testing, the robot again engages the panel or wafer and removes the panel or wafer from the test equipment and returns it to the cassette.
This presents several difficulties. Testing time includes time to remove the panel from the cassette and transport it to the test device, and the time required to remove the panel from the test device and return it to the cassette. Each time the panel or wafer is engaged or disengaged by handling equipment, such as the robot end effector or the handler of the test device, there is a risk of damage. The time required to position the sample or sheet before measurement or testing and replace the sample after measurement or testing is increased by the need to have several devices successively engage and release the wafer or panel.